1. Field of the Invention
The present invention relates to a coffee brewing apparatus, which is particularly used in an automatic coffee dispenser, and a method of brewing coffee by the apparatus.
2. Description of the Prior Art
One of popular coffee brewing methods is to pour hot water onto ground coffee so that the hot water extracts coffee ingredient while passing through the ground coffee. In a simple method, the hot water passes down through the ground coffee by its own gravity. There is also a conventional method in which the hot water is forced to pass through ground coffee.
FIG. 11 shows a conventional coffee brewing system used in an automatic coffee dispenser. The system includes a water supply line 310, a water shutoff valve 311, a water heater 312, a hot water supply line 313, a hot water shutoff valve 314, and a coffee brewing apparatus 300, which is shown in elavational section.
The coffee brewing apparatus 300 includes a hot water supply cylinder 301, a piston 302, a cylindrical ground coffee holder 303, a strainer 304 and a coffee outlet funnel 305. The top open end of the ground coffee holder 303 is removably and sealingly fitted to the bottom open end of the hot water supply cylinder 301. The strainer 304 is tightly interposed between the ground coffee holder 303 and the coffee outlet funnel 305. The piston 302 is adapted to sealingly and slidingly fit the hot water supply cylinder 301 internally.
A predetermined quantity of ground coffee 303c is deposited in the holder 303 before it is fitted to the hot water supply cylinder 301. The water provided through the water supply line 310 to the water heater 312 is heated up to a near boiling temperature at a regulated pressure. A predetermined quantity of hot water 301w is provided from the water heater 312 into the hot water supply cylinder 301 through the hot water supply line 313 by opening the hot water shutoff valve 314 for a predetermined time period. Then, the piston 302 is lowered into the cylinder 301 so that the hot water 301w in the cylinder 301 and most of the air trapped in the cylinder 301 are forced down through the ground coffee 303c in the holder 303. Then, the hot water extracts coffee ingredient from the ground coffee 303c while passing therethrough and comes out through the strainer 304 and the coffee outlet funnel 305, as shown by an arrow in FIG. 11.
Another popular conventional coffee brewing method is to deposit ground coffee into hot water and blow air into the mixture of the hot water and the ground coffee so that the ground coffee is agitated in the hot water. This method, however, is not adequate for producing strong coffee because it requires a comparatively large quantity of hot water per unit quantity of ground coffee.
Whereas some disadvantages are known pertaining to the method by the apparatus 300 shown in FIG. 11. Since the ground coffee 303c is loosely deposited in the ground coffee holder 303, granules of the ground coffee 303c tend to shift from one place to another in the holder as the hot water flows down in the holder. This results in a creation of a partial hot water flow path in the holder, which is known as "channeling". The channeling effect causes the ground coffee in the holder to be subjected to the hot water unevenly. Since the channeling occurs randomly in the holder, coffee liquid of varied density tends to be produced in each coffee making process. In the above described coffee brewing method by the apparatus 300, the hot water starts to flow down through the ground coffee as soon as the cylinder 301 starts receiving hot water before the piston 302 enters the cylinder 301 to force the hot water down. This early flow of hot water also causes undesirable "channeling" in the ground coffee.